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git merge in depth Anton Chikin

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test branch merge master to branch test branch merge branch to master test master

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test branch merge master to branch test branch merge branch to master test master WAT

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I don’t trust merge!

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No content

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No content

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3-way merge

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master

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master branch

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master branch

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master branch

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master branch

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master branch

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master branch ?

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master branch ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data

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? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data master branch

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? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data master branch ?

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? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data master branch ? ?

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? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data master branch ? ? ?

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? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data master branch ? ? ? ?

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? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data master branch ? ? ? ? Nearest common ancestor var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data

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? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor master branch

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? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch

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? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo”

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? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo”

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? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var data = {} for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) def getData(string path)

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? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var data = {} for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) def getData(string path)

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def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {}

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def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} ?????????????

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def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} ?????????????

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def getData(string path) <<<<<<< HEAD var data = Map() ||||||| merged common ancestors var data = {} ======= var data = Array() >>>>>>> branch

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def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} var data = Map() for l in visit(path)

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def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} var data = Map() for l in visit(path)

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def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} var data = Map() for l in visit(path) data[l.id] = l.data

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def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} var data = Map() for l in visit(path) data[l.id] = l.data

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def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} var data = Map() for l in visit(path) data[l.id] = l.data return data.JSON()

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def getData(string path) ? var a = “foo” def getData(string path) var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() var a = “foo” def getData(URI path) var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” def getData(string path) var data = {} for l in visit(path) data[l.slot] = l.data return data ancestor merge ancestor master branch var data = Map() for l in visit(path) data[l.slot] = l.data return data.JSON() for l in visit(path) data[l.slot] = l.data return data var data = Array() for l in visit(path) data[l.id] = l.data return data var a = “foo” var a = “foo” var a = “foo” var a = “foo” def getData(string path) def getData(URI path) var data = {} var data = Map() for l in visit(path) data[l.id] = l.data return data.JSON()

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master branch ?

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master branch

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master branch merge master into branch

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master branch merge master into branch

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branch merge branch into master master

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recursive 3-way merge

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master Let’s take a look at a more complicated picture

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master hotfix Let’s take a look at a more complicated picture

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master hotfix Let’s take a look at a more complicated picture

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master feature hotfix Let’s take a look at a more complicated picture

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master hotfix feature Let’s take a look at a more complicated picture

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master hotfix feature Let’s take a look at a more complicated picture

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master M hotfix feature Let’s take a look at a more complicated picture

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master M M hotfix feature Let’s take a look at a more complicated picture

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master M M ? hotfix feature Let’s take a look at a more complicated picture

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master M M ? hotfix feature Let’s take a look at a more complicated picture nearest common ancestor

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master M M ? hotfix feature How to deal with two nearest common ancestors? nearest common ancestor nearest common ancestor

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master M M ? hotfix nearest common ancestor Step 1: find nearest common ancestor of those ancestors

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master M M ? hotfix Step 2: merge them into “fake” commit nearest common ancestor

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master M M ? hotfix Step 3: Merge our commits using that “fake” ancestor nearest common ancestor

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master M M hotfix M nearest common ancestor This process can be recursive

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master M M hotfix feature M

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And what about rebase?

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master branch master A B C

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master branch master A B C nearest common ancestor Again, find NCO

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master branch master diff B diff C diff A A B C Create diffs between each commits starting from NCO

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master branch master A B C diff B diff C diff A Move branch head to master

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master branch master A B C A’ diff B diff C Apply each diff on top of latest master commit

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master branch master A B C A’ B’ diff C Apply each diff on top of latest master commit

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master branch master A B C A’ B’ C’ Apply each diff on top of latest master commit

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@1,1 - A + B What does it mean to “apply diff”? Diff format is quite simple: In the first line

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@1,1 - A + B Diff format is quite simple: In the first line replace “A” What does it mean to “apply diff”?

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@1,1 - A + B Diff format is quite simple: In the first line replace “A” with “B” What does it mean to “apply diff”?

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A B C @1,1 - A + B B B C What does it mean to “apply diff”?

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D B C @1,1 - A + B ???????? B C What if first line in file is not “A” but “D”? Same as in merge - conflict! What does it mean to “apply diff”?

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D B C @1,1 - A + B ???????? B C What if first line in file is not “A” but “D”? Same as in merge - conflict! What does it mean to “apply diff”?

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master branch branch master A’ B’ C’ A B C M Merge and rebase give you different branch structure but the same result

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Merge commits “train station”

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Merge commits “subway”

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Finally - don’t be afraid of recursive merge - merge a ->b == merge b ->a - merge == rebase - prefer merge over rebase - merge will never never let you down

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•http://think-like-a-git.net/ •http://git-school.github.io/visualizing-git/ Resources

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Questions?

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git merge in depth Anton Chikin